You should aim for 64-80 oz of juice per day while on the reboot.  Each mean green recipe makes about 24 oz. with a decent size cucumber. I typically had 4-5 mean greens per day, or 80-100 oz. of juice per day during my fast.

Aim for drinking 1/2 your current body-weight in ounces of water per day.  Water is important to keep things moving and to assist with the release of toxins.  Both are important, but if you are going fall short of target on something, you have some wiggle room on water.  Detox juices like the mean green are high in water content but they also serve as a diuretic.  This means good clean water will help you get the best results.

Hot water or (non-caffeinated) herbal tea (without sugar) is great.  During the cold months, I have found brewing some green tea with a 1/2″ of shaved ginger root, and the juice of half of lemon is a great morning pick me up.  Unless you are especially sensitive to low levels of caffeine you can enjoy green tea through lunchtime without sleep issues.